1. Field of the Invention
The present invention generally relates to mobile telephones such as cordless and cellular phones and specifically to those mobile telephones utilizing a speaker to convert electronic signals into acoustic signals.
2. Description of the Prior Art
Mobile telephones generally utilize a speaker to convert electronic signals representing verbal communication into acoustic communication signals as in a conventional telephone. Cordless and cellular phones generally have a "standby" mode (when the phone is not currently being used but when a call can be received) and an "active" mode of operation (when the phone is being used to generate a call or when a call has been answered). In many mobile telephones, a separate buzzer is utilized to generate a "ring" signal to indicate an incoming call to the operator when the phone is in the "standby" mode of operation (the equivalent of a conventional telephone when the receiver is on the cradle).
In order to be properly heard, the amplitude output of the buzzer in a mobile telephone has to be over 100 dBSPL at 1 cm distance. This sound level of signalling the ringing of the telephone would be very obnoxious in the event that the telephone were to ring when a user placed the phone to his or her ear.
Accordingly, prior art mobile phones utilized a separate buzzer and speaker. This also permitted the buzzer to be located near the end of the mobile telephone which conveniently would extend in an upward direction so that the buzzer could be easily heard during a "ring."
During the standby mode, the telephone operates only as a receiver and generates an appropriate "ring" signal when the base transmitter transmits the appropriate signal to the mobile telephone. The operational mode of the mobile telephone can be changed from "stand-by" to "active" by the operator keying a particular switch or opening the "flip" portion of the phone. Once changed to the active mode, the telephone will still ring but can also be used to generate a call (dial out) or to "answer" and converse with a party who has called in to the telephone.
It is desirable to reduce the costs of manufacturing such mobile telephones by reducing the number of parts and, if possible, reducing the area of required printed circuit boards by eliminating the buzzer and its associated circuitry. It has been proposed to use the loudspeaker as the generator of the acoustic "ring" signal. However, utilization of the speaker causes some difficulties in that, if the "ringing" signal generated by the speaker is sufficiently loud to signal the consumer that the phone is "ringing," this acoustic signal could also create discomfort and/or hearing damage in the operator of the mobile telephone if the phone "rang" when the operator has the phone in use, i.e., next to the operator's ear.
It is also desirable to eliminate the holes in the cover of a mobile telephone where such holes normally were in conjunction with the buzzer location to provide the maximums put during the "ringing" of the telephone. Unfortunately, the use of such holes provides an additional opening in the mobile telephone permitting impurities, dirt, water, etc. to enter the mobile telephone.